Process for analyzing mercury

ABSTRACT

A process for quantitatively analyzing mercury in incineratable samples which comprises heating a mercury-containing sample in the presence of oxygen to effect complete incineration of the sample and form a vapor containing atomic mercury, passing such vapor through a heated glass tube containing a basic salt, cooling the vapor, bringing the cooled vapor into contact with a metal capable of amalgamation to capture the mercury as an amalgam, heating the amalgam to regenerate mercury vapor and measuring the quantity of that vapor. According to this invention, the quantitative analysis of mercury can be attained rapidly and automatically in a simple and precise manner without application of a particular preliminary treatment.

United States Patent [191 Sugiyama [451 May 20, 1975 1 PROCESS FOR ANALYZING MERCURY [75] Inventor:

[73] Assignee:

[30] Foreign Application Priority Data Aug. 13, 1973 Japan 48-90702 [52] US. Cl 23/230 PC; 23/253 PC; 23/254 R [51] Int. Cl. G01n 7/08 [58] Field of Search 23/230 PC, 253 PC, 232 R,

23/232 E, 254 R, 254 E OTHER PUBLICATIONS Thomas et al., Rapid Pyrolytic Method to Determine COOLING TUBE Total Mercury in. Fish, ANAL. CHEM., Vol. 44, No. 3, March 1972, pp. 512-515.

Primary Examiner-R. E. Serwin Attorney, Agent, or FirmWilliam J. Daniel [57] ABSTRACT A process for quantitatively analyzing mercury in incineratable samples which comprises heating a mercury-containing sample in the presence of oxygen to effect complete incineration of the sample and form a vapor containing atomic mercury, passing such vapor through a heated glass tube containing a basic salt, cooling the vapor, bringing the cooled vapor into contact with a metal capable of amalgamation to capture the mercury as an amalgam, heating the amalgam to regenerate mercury vapor and measuring the quantity of that vapor. According to this invention, the quantitative analysis of mercury can be attained rapidly and automatically in a simple and precise manner without application of a particular preliminary treatment.

9 Claims, 2 Drawing Figures TO MERCURY l x -h l ANALYZER HEATERS WATER REMOVING ZONE BASIC SALT 1 6 Z HEATER i 4 l l seas/ 1 i l CARRIER GAS PATENT MAY20|975 F/GI AMALGAMATING ZONE COOLING TUBE R E H L A N A m M m E ER REMOVING ZONE SAMPLE VESSEL 2 HEATERS v BASIC SALT HEATER 4 PROCESS FOR ANALYZING MERCURY BACKGROUND OF THE INVENTION This invention relates to a process for analyzing mercury. More particularly, this invention relates to an analyzing process for quantitatively analyzing in a rapid and simple manner very small amounts of mercury contained in water samples, living bodies, mineral substances and air.

Hitherto, the quantitative analysis of mercury has been performed either by oxidizing a mercury containing substance to convert mercury in various forms into mercuric compounds which were then extracted with dithizone and subjected to colorimetry, or by reducing a mercury-containing substance with a strong reducing agent, such as a stannous salt or ascorbic acid, to liberate metallic mercury from the substance and then allowing the metallic mercury to evaporate for atomic spectrum absorptiometry. In the practice of these processes, however, a preliminary treat ment is required for decomposing the other ingredients present with a strong acid or a strong oxidizing agent to convert mercury into mercuric ions. This preliminary treatment has some disadvantages, viz., it takes a long period of time, up to l hours or more, and inevitably induces an analytical error due to vaporization of the mercury. In any event, vaporization of metallic mercury often results in analytical errors and is regarded in the prior art analyzing processes as one of the undesirable properties of metallic mercury.

The present inventor has already developed a process for quantitatively analyzing mercury which takes advantage of this normally undesirable property and uses the steps of completely incinerating a mercurycontaining sample to liberate therefrom atomic mer cury as vapor, bringing the mercury vapor into contact with a metal capable of amalgamation thereby capturing the mercury vapor as an amalgam, heating the amalgam to regenerate mercury vapor and measuring the quantity of that vapor. In comparison with prior art processes, this process is rather simple and advantageous in respect to treating time. In practicing this process, however, a part of an acidic incineration gas generated on incineration of a mercury-containing sample sticks onto the inner surface of the glass tubes which convey it and a carrier gas to analyzing instruments and condenses thereon as a slightly acidic liquid Accordingly, a certain quantity of the mercury liberated from the sample is eventually lost by adsorption to glass tubes before reaching the analyzing instruments. Thus, this process fails to measure the quantity of mercury precisely. On the other hand, a nitrogen-containing sample such as protein evolves oxides of nitrogen upon incinceration and a part of these oxides is adsorbed onto the surface of the amalgamating agent and is desorbed simultaneously with the liberation of mercury from its amalgam. When the mercury is measured according to atomic spectrum absorptiometry, such coexistent oxides of nitrogen will cause errors in measurement.

In recent years, it is becoming increasingly important to be able to rapidly analyze very small amounts of mercury contained in exhaust gas, waste water and organic matters. Thus, there is a real need for an analyzing process which fully meets these requirements.

BRIEF SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a process for quantitatively analyzing mercury in a rapid and simple manner.

It is another object of this invention to provide a process for analyzing mercury in various forms without the necessity for special preliminary treatment of the sample to be analyzed.

It is still another object of this invention to provide an automatic process for analyzing mercury without any necessity for manual operation.

It is a further object of this invention to provide a process for quantitatively analyzing very small amounts of mercury in gaseous, aqueous and solid samples.

It is still a further object of this invention to provide a new type of incineration apparatus for analyzing mercury.

Other objects, features and advantages of this invention will become apparent as the description proceeds.

DETAILED DESCRIPTION OF THE INVENTION As a result of much research aimed at overcoming the drawbacks in prior art processes, it has now been found that the adverse influence of the acidic incineration gas can be avoided by heating the glass tubes extending from the exit of the incineration furnace to a spiral cooling tube. This invention is based on this discovery.

In accordance with one aspect of this invention, there is provided a process for analyzing mercury which comprises heating a mercury-containing sample at a temperature of 400l,lOOC in the presence of oxygen to effect complete incineration of the sample into a vapor containing atomic mercury, passing the thus generated vapor through heated glass tubes containing a basic salt, cooling the vapor, bringing the cooled vapor into contact with a metal capable of amalgamation to capture the mercury as an amalgam, heating the amalgam to regenerate vapor of mercury and measuring the quantity of that vapor.

In the invention, the use of a basic salt serves to absorb the acidic incineration gas while heating of the glass delivery tube having the basic salt therein serves to prevent condensation of any liquid containing mercury, thus enabling the quantity of mercury to be measured precisely.

FIG. 1 is a schematic view of one example of apparatus for practicing the process of this invention.

FIG. 2 is a chart showing the results of analyses carried out in Example 1 according to the atomic spectrum absorptiometry vs the prior art and a control.

Referring to FIG. 1, a sample vessel 2 is filled with a sample to be analyzed and placed in the incineration zone 3 of an incineration tube. A carrier gas such as air or oxygen is introduced into the tube through a carrier gas inlet 1. Introduction of the carrier gas is attained by the aid of a diaphragm pump or compressor or by using a self-pressurized gas directly from a pressurized air bomb or oxygen bomb, none of which is shown, It is obvious that such carrier gas should previously be freed from mercury by any suitable means. The sample incineration zone 3 is composed, for example, of a quartz tube packed with a filler and is externally heated at 4001,100C, preferably 600850C by an appropriate electric mantle heater which may be switched in several steps, for example by four steps, so as to enable 3 variation of the heating range for providing an optimum incineration condition according to the type of sample. The sample is decomposed thermally by incineration in this zone and vaporized mercury is formed. When the sample is in the form of an aqueous solution, the rate of heating should be controlled so as to prevent bumping. Mercury compounds in various forms are decomposed by this incineration treatment, generating a vapor containing atomic mercury. A filler is usually charged into the incineration tube to promote complete incineration of the sample. Quartz wool is ordinarily used as the filler but, if desired, an oxidizing catalyst such as cupric oxide, cobalt oxides, platinum or palladium may also be used.

The gas formed by thermal decomposition is entrained in the carrier gas and passed through a zone 4 where a basic salt has previously been charged. Illustrative of the basic salt are carbonates of alkali and alkali earth metals, for example, potassium carbonate, so-

dium carbonate and barium carbonate. The acidic incineration gas is neutrallized by passage through this zone 4. The zone 4 is heated preferably at 200700C to prevent adsorption of mercury onto the basic salt. The incineration gas entrained in the carrier gas is then passed through a spiral cooling tube 5 and conveyed to a water elimination zone 6 where water vapor is condensed and separated from the gas. Cooling of the gas is effected by either water cooling or air cooling and the condensed water is vented out of the system. It is preferable to control the partial pressure of water vapor in the carrier gas which has passed through the water elimination zone 6 so that the partial pressure may be adjusted to less than the saturated water vapor pressure.

The gas freed from water is then conveyed to a mercury capturing zone 7 where metallic mercury contained in the gas is brought into contact with an amalgamating agent and captured as an amalgam. The mercury capturing agent is a metal capable of amalgamation and examples thereof include gold, silver, copper, cadmium, zinc, platinum and palladium. These metals may be used alone but may be carried on a heatresisting support such as quartz powder, diatomaceous earth or refractory brick powder. Mercury caught by the amalgamating agent in the zone 7 is then heated in situ and liberated as mercury vapor from the agent. The mercury vapor is again entrained in the carrier gas and conveyed to a mercury analyzer (not shown) where the quantity of mercury is measured by a suitable means known per se. For example, mercury vapor in the carrier gas is determined in the analyzer by measuring absorbance at a resonance line of 253.7 m,u.. Any type of conventional atomic spectrum absorptiometer or mercury analyzer can be used as the analyzer for this invention.

When a sample of a liquid, living body or mineral is subjected to analysis according to the process of this invention, the sample is charged into a sample vessel and then thermally decomposed in the incineration zone to form an incineration gas containing vaporized atomic mercury. For a gaseous sample, a definite volume of the gaseous sample is entrained in the carrier gas before introduction into the analyzer.

The process of this invention has the advantage that mercury compounds in various forms can be analyzed quantitatively within a very short period of time, say, within ten minutes, without any necessity for special preliminary treatment as in prior art processes. Moreover, the individual analyses can be carried out entirely automatically without manual operation. No special reagents are used so that the number of blank tests can be minimized. Finally, this invention makes possible the measurement of the quantity of mercury in samples in a very precise manner.

This invention will now be explained in more detail by way of the following examples.

EXAMPLE 1 In a quartz vessel were placed 50 mg of gelatin and 0.1 pg of mercury was added thereto. The quartz vessel was inserted into a heated glass tube which had been packed with sodium carbonate to neutralize the acidic gas. The gelatin sample was thermally decomposed in a stream of oxygen and the incineration gas was separated from condensed water and passed through an amalgamating agent in the form of platinum carried on diatomaceous earth where the vapor of atomic mercury in the incinerated gas formed an amalgam with the platinum. Then, the amalgamating agent was heated at 800C to regenerate atomic mercury vapor which was then subjected to atomic spectra absorptiometry. The results obtained are shown in Chart A of FIG. 2. For the purpose of comparison, the results obtained by a similar analysis without using sodium carbonate are shown in Chart B of FIG. 2. The results of a similar analysis using a 0.1 ,ug sample of mercury alone are also shown in Chart C of FIG. 2. In Chart B, the presence of oxides of nitrogen in addition to mercury is measured. In Chart A, however, only the mercury is measured and the result substantially matches that in Chart C. It is apparent that the use of an acidic gas neutralization according to this invention aids in the precise analysis of the quantities of mercury contained in organic substances.

EXAMPLE 2 Using a combination of the following apparatus, accuracy in quantitative analysis of mercury according to the process of this invention was tested: Incineration apparatus Model MV-250 (Sugiyama-Gen Environmental Services); Analyzer Model MV-253 (Toshiba-Beckmann; gain 10; span 6); Recorder Available from Nippon Denshi Kagaku (gain 0.1 V; speed 2.5 cm/min.).

An aqueous solution containing mercury in an.

TABLE 1 Ouan. Mercury (p.- liter I-Ig' Average stan. Soln. Height Height cont. 0.1 of Peak of Peak r g/m g) As is evident from the table, good linearity is obtained in the results of the tests, or, in other words, the result of the analyses varied proportionally with increases in the amount of mercury in the test samples.

EXAMPLE 3 The quantity of mercury in fish meat was measured by using the same apparatus and conditions as those described in Example 2 except that the incineration time was 5 minutes. In this test, meat of dab was used as the test sample. The results of the test are as shown in Table 2 below.

TABLE 2 Samp g Average No.

Hg (ppm) MALNIQ- The differences in results are considered to be ascribable to errors in sampling.

A similar test was conducted using fish meat to which mercury had been added in an amount of 0.005 ug/O.2 g. The results are shown in Table 3.

TABLE 3 The rate of recovery of the mercury can be obtained from these results according to the following equation, where A is the average of the values of Table 2 and the other symbols are indicated above:

Rate of recovery [(D A) X B ]/C X 100 The results are shown in the following Table 4.

LII

TABLE 4 No. of Tests Rate of Recovery I claim:

1. A process for quantitatively analyzing mercury which comprises heating a mercury containing sample in the presence of oxygen to effect complete incineration of the sample to form a vapor containing atomic mercury, passing such vapor through a heated glass tube containing a basic salt, cooling the vapor, bringing the cooled vapor into contact with a metal capable of amalgamation to capture the mercury as an amalgam, heating the amalgam to regenerate mercury vapor and measuring the quantity of the mercury vapor.

2. A process according to claim 1 wherein the sample is heated in the range of 4001,100C.

3. A process according to claim 1 wherein the incineration vapor is entrained in a carrier gas for passage through said tube.

4. A process according to claim 3 wherein the carrier gas is selected from the group consisting of oxygen and an oxygen-containing gas.

5. A process according to claim 1 wherein the basic salt is a carbonate of an alkali metal.

6. A process according to claim 1 wherein the metal capable of amalgamation is carried on a heat-resisting support.

7. A process according to claim 1 wherein the metal capable of amalgamation is platinum.

8. An incineration apparatus for analyzing organic samples for mercury which comprises a sample incineration zone provided with an external heating means and an inlet for a carrier gas, an acidic gas absorbing Zone receiving the gas from said incineration zone and provided with a basic salt and an external heating means, a cooling zone to condensate water from the incineration gas after passage through said absorbing zone, a mercury-capturing zone provided with a metal capable of amalgamation and an external heating means operable to heat theresultant amalgam for regenerating mercury vapor from the amalgam, and an outlet from said capturing zone for venting the carrier gas and for delivering said regenerated vapor to a mercury vapor measuring means.

9. An apparatus according to claim 8 wherein the sample incineration zone is filled with a filler.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 39 DATED MaY 1975 |NVENTOR(S) Yunosuke Sugiyama It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In item [73] in the heading of the patent:

Delete "Kabushiki Kaisha Sugiawa-Gen" and insert therefor -Kabushiki Kaisha Sugiyama-Gen Signed and Scaled this twenty-sixth D ay Of August 1975 Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (ummissimwr uflarenls and Trademarks 

1. A PROCESS FOR QUANTITATIVELY ANALYZING MERCURY WHICH COMPRISES HEATING A MERCURY CONTAINING SAMPLE IN THE PRESENCE OF OXYGEN TO EFFECT COMPLETE INCINERATION OF THE SAMPLE TO FORM A VAPOR CONTAINING ATOMIC MERCURY, PASSING SUCH VAPOR THROUGH A HEATED GLASS TUBE CONTAINING A BASIC SALT, COOLING THE VAPOR, BRINGING THE COOLED VAPOR INTO CONTACT WITH A METAL CAPABLE OF AMALGAM TO REGENERATE MERCURY VAPOR AMALGAM, HEATING THE AMALGAM TO REGENERATE MERCURY VAPOR AND MEASURING THE QUNATITY OF THE MERCURY VAPOR.
 2. A process according to claim 1 wherein the sample is heated in the range of 400*-1,100*C.
 3. A process according to claim 1 wherein the incineration vapor is entrained in a carrier gas for passage through said tube.
 4. A process according to claim 3 wherein the carrier gas is selected from the group consisting of oxygen and an oxygen-containing gas.
 5. A process according to claim 1 wherein the basic salt is a carbonate of an alkali metal.
 6. A process according to claim 1 wherein the metal capable of amalgamation is carried on a heat-resisting support.
 7. A process according to claim 1 wherein the metal capable of amalgamation is platinum.
 8. An incineration apparatus for analyzing organic samples for mercury which comprises a sample incineration zone provided with an external heating means and an inlet for a carrier gas, an acidic gas absorbing zone receiving the gas from said incineration zone and provided with a basic salt and an external heating means, a cooling zone to condensate water from the incineration gas after passage through said absorbing zone, a mercury-capturing zone provided with a metal capable of amalgamation and an external heating means operable to heat the resultant amalgam for regenerating mercury vapor from the amalgam, and an outlet from said capturing zone for venting the carrier gas and for delivering said regenerated vapor to a mercury vapor measuring means.
 9. An apparatus according to claim 8 wherein the sample incineration zone is filled with a filler. 